IEC TS 62788-2:2024
(Main)Measurement procedures for materials used in photovoltaic modules - Part 2: Polymeric materials - Frontsheets and backsheets
Measurement procedures for materials used in photovoltaic modules - Part 2: Polymeric materials - Frontsheets and backsheets
IEC TS 62788-2:2024 defines test methods and datasheet reporting requirements for safety and performance-related properties (mechanical, electrical, thermal, optical, chemical) of non‑rigid polymeric materials intended for use in terrestrial photovoltaic modules as polymeric front- and backsheets. The test methods in this document define how to characterize front- and backsheet materials and their components in a manner representative of how they will be used in the module, which eventually includes combination with other matched components such as encapsulants or adhesives. Results of testing described in this document are called by IEC 62788-2-1 for safety qualification of polymeric front- and backsheets on component level and support the safety and performance-related tests defined on the PV module level as defined in the series IEC 61730 (for safety) and IEC 61215 (for performance). This document also defines test methods for assessing inherent material characteristics of polymeric front- and backsheets or their components, which can be required in datasheet reporting or can be useful in the context of product development or design of PV modules.
This second edition cancels and replaces the first edition published in 2017. This edition includes the following significant technical changes with respect to the previous edition:
a) With revision of IEC 61730-1 the requirements for the polymeric front- and backsheet have been moved from IEC 61730-1 into IEC 62788-2-1. This is reflected accordingly.
b) The tensile testing method has been refined based on findings of round robin tests, including updated drawings.
c) A thermal pre-exposure method has been introduced to be equivalent to the thermal effects of a "lamination" cycle. This pre-exposure defines the "fresh" state of the front- or backsheet in final application for evaluation of changes in ageing tests. For practical reasons, an oven exposure has been defined as an equivalent test.
d) The multiple functions of the lamination protrusion test (previously DTI test) have been clarified, to identify and measure RUI layer thickness as well as to identify layers for which the comparative tracking index (CTI) needs to be determined. Also the content of IEC 62788-2-1 has been updated, by which the lamination protrusion test and MST 04 are additionally set in perspective to each other via engineering judgement.
e) The DC breakdown voltage test method has been updated and the option to perform a withstand voltage test has been added (to reduce the required measurement voltage). The correction of DC breakdown voltage ( ) measurements, needed in the presence of non‑RUI layers and after the lamination protrusion test, has been defined more precisely.
f) Details for thickness measurement have been added (engineered surface roughness due to embossing).
g) The adhesion test methods have been reviewed and updated. The single cantilevered beam test has been added. Figures have been updated to align with IEC 62788-1-1.
h) The thermal failsafe test has been added as a test method based on discussion in the parallel project for IEC 62788-2-1. The test method offers a single temperature-point evaluation to include elongation at break to the thermal endurance evaluation.
I) A sequential UV/TC test ("solder bump test") has been added.
General Information
Relations
Standards Content (Sample)
IEC TS 62788-2 ®
Edition 2.0 2024-07
TECHNICAL
SPECIFICATION
Measurement procedures for materials used in photovoltaic modules –
Part 2: Polymeric materials – Frontsheets and backsheets
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.
IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews, graphical symbols and the glossary.
committee, …). It also gives information on projects, replaced With a subscription you will always have access to up to date
and withdrawn publications. content tailored to your needs.
IEC Just Published - webstore.iec.ch/justpublished
Electropedia - www.electropedia.org
Stay up to date on all new IEC publications. Just Published
The world's leading online dictionary on electrotechnology,
details all new publications released. Available online and once
containing more than 22 500 terminological entries in English
a month by email.
and French, with equivalent terms in 25 additional languages.
Also known as the International Electrotechnical Vocabulary
IEC Customer Service Centre - webstore.iec.ch/csc
(IEV) online.
If you wish to give us your feedback on this publication or need
further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC TS 62788-2 ®
Edition 2.0 2024-07
TECHNICAL
SPECIFICATION
Measurement procedures for materials used in photovoltaic modules –
Part 2: Polymeric materials – Frontsheets and backsheets
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8872-6
– 2 – IEC TS 62788-2:2024 © IEC 2024
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 10
4 Test procedures . 13
4.1 General . 13
4.1.1 Purpose . 13
4.1.2 Sample pre-treatment . 14
4.1.3 Type of sample constructions . 15
4.2 Mechanical characteristics . 16
4.2.1 General . 16
4.2.2 Thickness . 16
4.2.3 Area weight . 17
4.2.4 Tensile properties . 17
4.3 Adhesion testing . 21
4.3.1 Purpose . 21
4.3.2 General . 21
4.3.3 Specific use cases . 22
4.3.4 Methods . 24
4.3.5 Reporting requirements . 29
4.4 Thermal characteristics . 30
4.4.1 Thermal endurance . 30
4.4.2 Thermal failsafe test . 31
4.4.3 Dimensional stability . 32
4.4.4 Relative thermal expansion . 34
4.4.5 Thermal conductivity . 34
4.5 Electrical characteristics and insulation thickness . 35
4.5.1 Breakdown voltage . 35
4.5.2 Lamination protrusion test (aka DTI test) . 40
4.5.3 Comparative tracking index (CTI) . 43
4.5.4 Volume resistivity . 44
4.6 Optical characteristics . 45
4.6.1 General . 45
4.6.2 Specimen preparation . 46
4.6.3 Visual inspection . 46
4.6.4 Optical transmittance . 47
4.6.5 Optical reflectance . 48
4.6.6 Yellowness index . 48
4.6.7 Colour measurement . 49
4.6.8 Surface gloss. 50
4.7 Diffusion characteristics . 51
4.7.1 Permeability of water vapour . 51
4.7.2 Permeability of oxygen . 52
4.8 Chemical characteristics . 52
4.8.1 Resistance to solvents . 52
4.9 Other characteristics . 54
4.9.1 Ignitability – Purpose . 54
4.9.2 Flammability – Purpose . 54
4.10 Accelerated ageing tests . 54
4.10.1 Purpose . 54
4.10.2 Damp-heat ageing test . 55
4.10.3 UV weathering . 56
4.10.4 Abrasion test . 61
4.11 Sequential UV/TC stress test ("solder bump test") . 61
4.11.1 Purpose . 61
4.11.2 Sample construction . 62
5 Uniform characterization form . 68
5.1 General . 68
5.2 Layer stack description . 68
5.3 Material test results and reporting requirements. 68
6 Data sheet . 70
6.1 Purpose . 70
6.2 Reporting requirements . 70
7 Product identification sheet (label) . 70
Annex A (normative) Sample preparation . 71
A.1 Purpose . 71
A.2 Sample constructions . 71
A.2.1 General considerations . 71
A.2.2 Materials and procedures . 71
A.2.3 Overview of sample pre-treatments . 77
Annex B (informative) Overview of adhesion testing of front- and backsheets . 79
B.1 General . 79
B.2 Type of adhesion failure . 79
B.3 Characteristics of peel tests . 80
B.4 Characteristics of pluck and lap-shear tests . 80
B.5 Characteristics of cross-hatch tape test . 81
B.6 Characteristics of single cantilevered beam (SCB) test . 81
B.7 Other caveats . 81
Annex C (informative) Abrasion testing . 84
C.1 Purpose . 84
C.2 Methods . 84
Annex D (informative) Visual examination after sequential UV/TC stress test . 85
D.1 General . 85
D.2 Airside inspection of backsheet in reflection mode . 85
D.2.1 General . 85
D.2.2 Unexposed samples . 85
D.2.3 Airside: Rating of 1 . 86
D.2.4 Airside: Rating of 2 . 87
D.2.5 Airside: Rating of 3 . 87
D.2.6 Airside: Rating of 4 . 88
D.3 Glass side inspection of backsheet in transmission mode . 89
D.3.1 Unexposed samples . 89
D.3.2 Glass-side: Rating of A . 89
D.3.3 Glass-side: Rating of B . 90
D.3.4 Glass-side: Rating of C . 91
– 4 –
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.